1. Field of the Invention
The present invention relates to a message transfer apparatus that transfers a message while ensuring Quality of Service (QoS), an output method, and a computer program product.
2. Description of the Related Art
The QoS has been known as a technique that enables to ensure transmission quality in a network. In an IP network, the QoS is applied at the time of transmitting high-definition movie or speech. Accordingly, a network satisfying certain criteria with respect to quality conditions such as a transmission band, a transmission delay, and a packet discarding rate can be constructed.
Generally, the QoS is realized by a communication terminal (node) equipped with a QoS function. For example, when the node transmits a packet to the network and when the node processes the packet, priority of processing is determined for each packet. Because the packet is processed in decreasing order of the priority, the QoS with respect to a specific communication can be realized.
To make the QoS work correctly and ensure desired communication quality, processing for detecting a packet to be applied with the QoS and determination of a rule to be applied to the packet are essential.
JP-A 2008-35510 (KOKAI) proposes a technique that enables to start application of the QoS automatically when a PLC (power line communication) adapter detects a packet to be applied with the QoS in a home network using the PLC. JP-A 2008-35510 (KOKAI) also discloses that when the QoS cannot be applied, that effect is notified, for example, by blinking a light emitting diode (LED) of the PLC adapter.
JP-A 2006-174350 (KOKAI) proposes a technique that enables to realize the QoS by using an identification condition and a processing rule of a packet group preset or downloaded from a network to detect a packet satisfying the identification condition from packets passing through a node, and apply the processing rule to the detected packet.
However, according to the conventional methods disclosed in JP-A 2008-35510 (KOKAI) and JP-A 2006-174350 (KOKAI), there is a case that the QoS cannot be applied appropriately to a node requesting application of the QoS. This is because applicability of the QoS is determined mainly according to an internal condition of an apparatus that realizes the QoS such as an available band or an available storage area, in the conventional methods.
That is, in such methods, applicability of the QoS cannot be determined according to an external condition of the node, for example, how the network to which a node requesting application of the QoS belongs is connected to other nodes. Therefore, the QoS satisfying the request may not be realized depending on operating states of other nodes connected to the same network.
For example, it is assumed that a local area network (LAN) formed of the Ethernet (registered trademark) is connected to a wired area network by a router having the QoS function. In this case, when communication with the QoS being ensured arrives from the wide area network, the router can transfer the communication to the LAN while maintaining the QoS. However, when a node transmitting a large number of packets is connected to the LAN, communication disturbance is likely to occur due to the packets in the LAN, even if the router transfers the packet in an appropriate condition. As a result, the QoS cannot be applied.
Thus, when the node which performs QoS communication and the node which performs best-effort communication are connected together, each node may not be able to obtain desired communication quality. Further, not only the QoS cannot be applied, but also the best-effort communication may be completely inhibited in a case that many QoS nodes are connected.
Such problems occur because the QoS is set regardless of a topology of the LAN. Particularly, the problem is that the node performs communication in an environment, which is not assumed by a service provider who provides service by using the QoS communication.
Further, users having no technical knowledge of the network and computers can hardly understand that there is a problem in the network topology. For example, the user can hardly investigate the cause of a situation in which the movie and speech are disturbed, although all the nodes are connected to the LAN in the same manner and communication is possible.